DDEC III/IV Single ECM Troubleshooting – Section 21.3 Troubleshooting Flash Code 21

Section 21.3
Troubleshooting Flash Code 21

The following procedure will troubleshoot Flash Code 21.‪

Section 21.3.1
Multiple Code Check

Perform the following steps to check for multiple codes.‪

1. Turn ignition ON.
2. Plug in DDR.
3. Read active codes.
   1. If active code 91/3 and no other active codes are logged, refer to "21.3.2 Sensor Check" .
   2. If any or all of the following codes are logged, 91/3, 91/4, 187/3, 100/3, refer to "91.2 Troubleshooting Vehicle Harness +5 Volt Supply" .
   3. If any codes except 91/3 are logged, refer to "21.3.3 Return Circuit Check" .

Section 21.3.2
Sensor Check

Perform the following steps to check the sensor.‪

1. Turn ignition OFF.
2. Unplug the TPS connector.
3. Turn ignition ON.
4. Read for active codes.
   1. If active code 91/3 and any other codes are logged, refer to "21.3.7 Check for Short" .
   2. If code 91/4 is logged, refer to "21.3.3 Return Circuit Check" .

Section 21.3.3
Return Circuit Check

Perform the following steps to check the return circuit.‪

1. Turn ignition OFF.
2. Install a jumper wire between pin A (return #952) and pin B (signal #417) of the TPS harness connector.
3. Disconnect the vehicle harness connector at the ECM.
4. Measure resistance between sockets C3 and D2 on the vehicle harness connector. For Throttle Position Sensor schematic, See figure "Throttle Position Sensor" .
   1. If the resistance measurement is less than or equal to 5 Ω, refer to "21.3.4 Check Throttle Position Sensor Adjustment" .
   2. If the resistance measurement is greater than 5 Ω, and the return line #952 is open, repair the open and refer to "21.3.10 Verify Repairs" .
   

   Figure 1. Throttle Position Sensor

Section 21.3.4
Check Throttle Position Sensor Adjustment

Perform the following steps to check for TPS adjustment.‪

1. Reconnect vehicle harness connector and plug in the TPS.
2. Hook up DDR to the DDL connector and select Throttle Sensor Display.
3. Measure Throttle Counts at both no throttle and full throttle. Take several readings.
   1. If TPS counts are ever greater than 968 counts, refer to "21.3.5 Throttle Position Sensor Adjustment" .
   2. If TPS counts stay less than 968 counts, refer to "21.3.6 Check Throttle Position Sensor Connectors" .

Section 21.3.5
Throttle Position Sensor Adjustment

Perform the following steps to attempt TPS adjustment.‪

1. Check for pedal or linkage interferences.
2. Loosen the TPS screws and attempt to adjust for the correct throttle reading (64 - 205 counts). Do not attempt to adjust by bending the pedal mechanism.
3. Recheck counts at idle and at full throttle.
   1. If the throttle counts are not correct, refer to "21.3.6 Check Throttle Position Sensor Connectors" .
   2. If the throttle counts are now correct, refer to "21.3.10 Verify Repairs" .

Section 21.3.6
Check Throttle Position Sensor Connectors

Perform the following steps to check the TPS connectors.‪

1. Check terminals at the TPS connector (both sensor and harness side) for bent, corroded and unseated pins or sockets. See Figure "Throttle Position Sensor" .
   1. If the terminals or connectors are damaged, repair both and refer to "21.3.10 Verify Repairs" .
   2. If the terminals or connectors are not damaged, replace the TPS; refer to "21.3.10 Verify Repairs" .
   

   Figure 2. Throttle Position Sensor

Section 21.3.7
Check for Short

Perform the following steps to check for a short.‪

1. Turn ignition OFF.
2. Disconnect the vehicle harness connector at the ECM. Unplug the TPS connector.
3. Read resistance between sockets D2 and A3 on the vehicle harness connector. For ECM vehicle harness connector, see Figure "ECM Vehicle Harness Connector" .
   1. If the resistance is greater than 100 Ω or open, refer to "21.3.8 Check for Short to Battery" .
   2. If the resistance is less than or equal to 100 Ω, the signal line (#417) is shorted to the vehicle +5 volt line (#916). Repair the short and refer to "21.3.10 Verify Repairs" .
   

   Figure 3. ECM Vehicle Harness Connector

Section 21.3.8
Check for Short to Battery

Perform the following steps to check for a short to the battery.‪

1. Remove both fuses to the ECM.
2. Disconnect the 5-way power harness and vehicle harness connectors at the ECM.
3. Measure resistance between socket D2 on the vehicle harness connector and the 5-way power connector sockets A and C. See Figure "5-Way ECM Power Connector" .
   1. If the resistance is greater than 100 Ω, refer to "21.3.9 Check ECM Connectors" .
   2. If the resistance is less than or equal to 100 Ω, a short exists between sockets where less than 100 Ω resistance was read. Repair short and reinsert fuses. Refer to "21.3.10 Verify Repairs" .
   

   Figure 4. 5-Way ECM Power Connector

Section 21.3.9
Check ECM Connectors

Perform the following steps to check the ECM connectors.‪

1. Check terminals at the ECM harness connector (both ECM and harness side) for bent, corroded and unseated pins or sockets. See Figure "ECM Vehicle Harness Connector" .
   1. If terminals and connectors are damaged, repair them. Refer to "21.3.10 Verify Repairs" .
   2. If terminals and connectors are not damaged, refer to "21.3.10 Verify Repairs" , to review this section. If review leads back here, install a test ECM or contact Detroit Diesel Technical Service.
   

   Figure 5. ECM Vehicle Harness Connector

Section 21.3.10
Verify Repairs

Perform the following steps to verify repairs.‪

1. Turn ignition OFF.
2. Reconnect all connectors.
3. Turn ignition ON.
4. Clear DDR codes.
5. Start and run the engine for one minute. Check idle position and full throttle.
6. Stop engine.
7. Check DDR for codes.
   1. If no codes are displayed, troubleshooting is complete.
   2. If code 91/3 is not logged, and other codes are logged, refer to "9.1 First Step for Diagnosing a Fault Within the DDEC System" .
   3. If code 91/3 is logged, and other codes are logged, all system diagnostics are complete. If a problem still exists, review this section from the first step to troubleshoot the error, refer to "21.3.1 Multiple Code Check" .